When crude oil and other oils are stored for a long time in storage tanks, solid oil components thereof separate and accumulate in the form of sludge in the bottoms of the tanks. The sludge decreases the inner volume of the storage tank and interferes with maintenance and inspection of the tank interior and, therefore, must be removed from the tank interior.
In the disposal of sludge, when the amount of sludge so accumulated is small, as when the mound of sludge accumulated has not risen above the manholes provided in the lower portion of the lateral wall of the tank, for example, required removal of the accumulated sludge can be effected by first removing the oil from the tank interior, then opening the manholes, and introducing devices for the removal of sludge through the opened manholes into the tank interior. The removal of sludge by this method, however, becomes difficult when the mound of accumulated sludge rises above the manholes and the manholes can not be opened.
In this case, the ordinary method adopted for the disposal of sludge comprises heating the sludge by some means to a temperature exceeding the fluidifying temperature of the sludge and extracting the fluidified sludge out of the tank by means of a pump.
Recently, there have appeared large oil storage tanks having inner volumes ranging from 50,000 to 150,000 m.sup.3. They at times suffer accumulation of as much as 20,000 to 50,000 kl of sludge in their interiors. For such large amounts of sludge to be heated to above the fluidifying temperature (50.degree. to 70.degree. C.), hinge quantities of thermal energy and much heating time are required. The heating, therefore, is very costly. Besides, the heating must be continued over a long time and prevents the tank interior from use while the work is in process. Moreover, this work is not feasible in the absence of a suitable heat source.
A method designed to remove the sludge by inserting a flexible pipe into the tank interior, spurting compressed oil through the leading end of the pipe, and disintegrating the sludge by the force of the spurted compressed oil has been disclosed in Japanese Patent Application Disclosure No. SHO 54(1979)-140260, for example.
In accordance with this method, however, the direction in which the flexible pipe spurts the compressed oil is not stable. Since the disintegration of the sludge is not efficiently effected, the work involved is prlonged to a great extent. The requirement that the sludge should be thoroughly disposed of in a short period of time can hardly be fulfilled by this method.
Japanese Patent Application Disclosure No. SHO 56(1981)-84675 discloses a spurting nozzle of a construction such that the nozzle body is inserted into a floating roof type oil storage tank through an aperture in a support column for the floating roof and the terminal portion of the nozzle is revolved around the nozzle body.